The present invention claims priority from Japanese Patent Application No. 11-290518 filed Oct. 13, 1999, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a display device capable of displaying a color image and an information terminal using the same display device and, particularly, to a display device for displaying an image by using liquid crystal and an information terminal such as portable telephone set in which the same display device is incorporated to display an information.
2. Description of Related Art
With the development of the digital technology and the communication technology, the multi-media industries handling data containing moving picture and voice have been expanding at high rate. For example, most of electronic devices such as portable telephone sets and mobile personal computers can be connected to other electronic devices or servers through cables or radio wave to take in or transmit various information. In the following description, not only the portable telephone set or PHS (Personal Handy-phone System) but also all of electronic devices functioning as terminals will be defined as information terminals and the term xe2x80x9cinformation terminalxe2x80x9d will be used in the above meaning.
Most of the information terminals include displays as devices for displaying information visually. Although a CRT (Cathode Ray Tube) has been used mainly for that purpose, there is a problem that the CRT is large in not only space occupation but also power consumption. In view of this fact, a liquid crystal display has been used in a portable information terminal driven by a battery. The liquid crystal display is featured by that it is possible to substantially reduce power consumption compared with the CRT.
Among the liquid crystal displays, a monochromatic liquid crystal display is advantageous compared with a color liquid crystal display in that the power consumption can be reduced substantially. The reason for this is that a drive circuit for a monochromatic display is simple enough to display a monochromatic image and, when a fine gradation of image is not required, the drive circuit can be further simplified. Further, it may be possible to eliminate a back-light for enabling a display even in a dark area.
On the contrary, in a display for displaying a color image, the image is displayed by using three primary colors RGB (Red, Green and Blue). Therefore, drive circuits corresponding to these primary colors are required, whose circuit constructions become complicated and consume power correspondingly when many tones are to be displayed. Further, in order to display an image with natural color including many color tones, it is necessary to always light a back-light for illuminating a rear side of liquid crystal with enough brightness thereof. In view of this fact, it is usual to use the monochromatic liquid crystal display in a device such as portable telephone set which is small in size and whose battery capacity is small.
FIG. 7 shows an example of a construction of a color liquid crystal display for use in a portable telephone set as a conventional information terminal capable of receiving multi-media, which is disclosed in JP-A 6-301032, color liquid display 100 is constructed with color light radiation source 101, liquid crystal display panel 102 and liquid crystal shutter 103 arranged between color light sources 101 and liquid crystal display panel 102. Color light radiation source 101 is constructed with color light sources 101R, 101G and 101B such as fluorescent lamps, tungsten lamps or CFL tubes corresponding to the three primary colors. In a case where these light sources are candescent light sources, three primary color filters are provided in front of these light sources, respectively. When color light sources 101R, 101G and 101B are ON/OFF controlled frequently corresponding to colors of an image, there is a problem that the life of color light radiation source 101 composed of fluorescent lamps, etc., is shortened. When the color light radiation source 101 is composed of tungsten lamps, there is a problem that the response to a color change is degraded.
In view of these problems, liquid crystal shutters 103R, 103G and 103B are arranged correspondingly to respective color light sources 101R, 101G and 101B and ON/OFF controlled. Lights selectively passed through liquid crystal shutters 103R, 103G and 103B radiate liquid crystal display panel 102 and a desired color image is displayed by synthesis of these three primary colors.
As mentioned above, in conventional color liquid crystal display 100, all of color light sources 101R, 101G and 101B corresponding to the respective three primary colors are lit when a color display is performed. This is also true when a monochromatic display is performed. Therefore, there is a problem that the power consumption of color liquid crystal display 100 is substantially increased compared with the display, which can display only monochromatic image.
FIG. 8 shows a construction of a display portion of an information terminal having reduced power consumption. Display portion 120, which is disclosed in JP-A 10-63196, is constructed with color liquid crystal portion 121 and monochromatic liquid crystal portion 122. Color liquid crystal portion 121 displays only moving image with color and monochromatic liquid crystal portion 122 displays other images. Therefore, when other information such as text information than a moving image information is displayed, monochromatic liquid crystal portion 122 is used and light sources of color liquid crystal portion 121 are turned OFF to reduce the power consumption.
FIG. 9 is a perspective view of another example of an information terminal having reduced power consumption, showing an outer configuration thereof and FIG. 10 is a side view of the same information terminal. In these figures, information terminal 131 includes main body portion 133 on a surface of which keyboard 132 is provided and cover portion 134. As shown in FIG. 10, cover portion 134 is hinged about rotary joint portion 135 such that either one of surfaces thereof can be looked from the side of keyboard 132. Color liquid crystal portion 136 is incorporated in one of the surfaces of cover portion 134 and monochromatic liquid crystal portion 137 is incorporated in the other surface. A display drive portion, which is not shown, provided within main body portion 133 performs a display control such that only one of the liquid crystal portions, which faces to the side of keyboard 132, is activated. Therefore, a user of information terminal 131 wishes a color image display, he turns cover portion 134 to provide color liquid crystal portion 136 on the side of keyboard 132. When the user wishes to see a monochromatic image in order to reduce power consumption or for other reasons, he turns the cover portion to provide monochromatic liquid crystal portion 137 on the keyboard side.
As described, since, in the case of color liquid crystal display 100 shown in FIG. 7, it is impossible to reduce power consumption even when the monochromatic display is performed, it has been usual to reduce power consumption by providing the color liquid crystal display portion and the monochromatic liquid crystal display portion as shown in FIG. 8 or FIG. 10. With such construction, it becomes unnecessary to light all of the light sources for the three primary colors for the monochromatic display to thereby make a use of one kind of light source such as candescent light source possible. However, since either one of the prior art information terminals has to equip with two kinds of liquid crystal displays, there is a problem that the manufacturing cost of the information terminal is substantially increased.
Further, in the information terminal shown in FIG. 8, it is necessary to arrange color liquid crystal portion 121 and monochromatic liquid crystal portion 122 in an upper portion of the main body thereof. Therefore, there is a problem that, although it is necessary to increase the size of the information terminal or reduce the sizes of liquid crystal portions 121 and 122, the usability of the information terminal is degraded.
In the case of information terminal 131 shown in FIG. 9 and FIG. 10, since the liquid crystal portion can be rotated by rotary joint portion 135, it is possible to make the information terminal itself compact. However, since the liquid crystal portion, which is not used, is exposed externally, there is a possibility of that portion damaged. Further, further, sine it is necessary to rotate cover portion 134 every time when the image display is switched between the color display and the monochromatic display, there is a problem that the switching operation is troublesome.
An object of the present invention is to provide a display device capable of displaying both a color image and a monochromatic image by means of a single display while reducing power consumption for the monochromatic image display and an information terminal using the same display device.
According to a first aspect of the present invention, a display device comprises:
(1) a back light as a light source for illuminating a predetermined surface from a back side thereof;
(2) color image reproducing means arranged on the surface illuminated by the back light, for outputting a color image synthesized with three primary colors by controlling amounts of transmission of the three primary color lights in respective two dimensional areas corresponding to an image signal; and
(3) monochromatic image reproducing means arranged on the surface illuminated by the back light, for outputting a monochromatic image by controlling an amount of transmission of light in respective two dimensional areas corresponding to an image signal.
That is, on the surface illuminated by the back light, the color image reproducing means outputting a color image synthesized with three primary colors by controlling amounts of transmission of the three primary color lights in respective two dimensional areas corresponding to an image signal and the monochromatic image reproducing means for outputting a monochromatic image by controlling an amount of transmission of light in respective two dimensional areas corresponding to an image signal arranged and, when the monochromatic image is displayed, the color image reproducing means is not driven. Further, even when a color image is displayed, a monochromatic image display can be simply combined with the color image.
The color image reproducing means and the monochromatic image reproducing means are transmission type liquid crystals having reflection type characteristics concurrently and the display device can further comprise back light drive control means for extinguish the back light except when a color gradation display is performed. With such back light drive control means, it is possible to reduce power consumption by extinguishing the back light in even color image display except the case where the color image is displayed with gradation.
Each of the color image reproducing means and the monochromatic image reproducing means may comprise a display electrode group composed of three kinds of rod like color electrodes for independently controlling displays of the respective R, G and B colors and one kind of rod like monochromatic display electrode for controlling a display of a monochromatic image, which are repeatedly arranged in predetermined directions on a common plane, a gate electrode group composed of a plurality of parallel gate electrodes arranged in a direction crossing the directions of the respective electrodes constituting the display electrode group with a predetermined interval and liquid crystal filling a space between the display electrode group and the gate electrode group. By repeatedly arranging four kinds of electrodes, that is, R, G and B color electrodes and the monochromatic electrode, a display control of each pixel becomes possible by a matrix arrangement of the pixels and the gate electrodes.
According to a second aspect of the present invention, an information terminal using the display device according to the first aspect of the present invention comprises:
(1) a display device including a back light as a light source for illuminating a predetermined surface from a back side thereof, color image reproducing means arranged on the surface illuminated by the back light, for outputting a color image synthesized with three primary colors by controlling amounts of transmission of the three primary color lights in respective two dimensional areas corresponding to an image signal and monochromatic image reproducing means arranged on the surface illuminated by the back light, for outputting a monochromatic image by controlling an amount of transmission of light in respective two dimensional areas corresponding to an image signal;
(2) receiving means for receiving data;
(3) data separation means for separating the data received by the receiving means to sound data and image display data; and
(4) display data separation means for further separating the image display data separated by the data separation means to message data represented by binary value and color data representing respective primary colors and supplying the message data and the color data to the display device as an image signal for monochromatic image and an image signal for color image.
In this information device, the received data is separated to the sound data and the image display data and the image display data is further separated to the message data represented by binary value and the color data representing the three primary colors and supplied to the display device. With this construction, it is possible to perform a control for superposing message on a color image easily.